(1) Field of the Invention:
This invention relates to a process for preparing a printed-circuit board, and more particularly to an improved process for preparing a printed-circuit board, the improvement comprising coating an electrodeposition coating composition containing a reduction type leico pigment on the surface of the copper foil of a copper-clad laminated plate for use in the printed circuit board (hereinafter referred to a copper-clad laminated plate) to form a photo-sensitive resist film thereon, followed by lapping a photographic negative or positive film onto the photo-sensitive resist film, and exposing to an active light such as laser, ultraviolet light, X-ray, electron beam or the like all over the photo-sensitive film or scanning the active light for drawing along a circuit pattern to develop a color as the circuit pattern is so as to make it possible to greatly reduce a reject rate of the product.
(2) Description of the Prior Art:
The printed-circuit board has conventionally been prepared for a long period of time by a process which comprises forming a photo-sensitive resist film on the surface of a copper foil of the copper-clad laminated plate, exposing the resist film to light through a desired pattern mask, followed by applying a developing treatment to obtain a resist film pattern, and applying etching onto the surface of an exposed copper foil to obtain a desired circuit pattern.
The conventional method of forming the photo-sensitive resist film on the copper foil on the surface of the copper-clad laminated plate includes a method of coating a liquid resist material by use of the conventional coating process such as dipping, roller coating, centrifugal coating and the like, a method of laminating a film-shaped photo-sensitive film called the dry film, for example, Riston film marketed by Du Pont de Nemours & Co. by use of the exclusive sticker, and the like. Recently, however, in place of the above conventional methods, there has been proposed a method of forming the photo-sensitive resist film which comprises coating a photo-curable electrodeposition coating composition (Japanese patent application Laid-Open No. 198795/86, etc.).
The method of forming the photo-sensitive resist film by coating the photo-curable electrodeposition coating composition on the copper foil on the surface of the copper-clad laminated plate has such advantages as to be capable of uniformly coating without loss of the starting material and of being incorporated into an automatic line.
However, the resist film formed after exposing the photosensitive resist film to light shows no change in appearance between before and after exposure to light and it is impossible for the resist film to distinguish an exposed area from an unexposed area, resulting in causing such defectives that exposure to light is doubly carried out, that the photo-sensitive resist film may be considered by mistake to have been exposed to light in spite of not having actually been exposed to light and may be subjected to the following development without exposing to light, resulting in forming no pattern resist film, and the like.
On the other hand, incorporation of a coloring matter such as dye or pigment into the electrodeposition coating composition results in reducing permeability to light through the film, in greatly reducing the productivity of the printed circuit board, and in causing such a disadvantage that the energy necessary to exposure to light must be increased in order to increase the above productivity.